The designer has tried to indicate on the schematic the way the grounds should be separated, and done a reasonable job with the standard symbols available to him.
There ought to be a detailed description and written guidelines in the datasheet, and recommended PCB layouts either there, or in a separate Application Note (if you look up this chip on the TI website, the relevant App Notes should be easy to find)
But basically, the IC contains both a high gain amplifier with a sensitive input, and a high current switch, capable of generating a lot of noise. With incorrect grounding, high currents in the ground wires can generate unwanted signals on the amplifier input, causing instability or poor voltage regulation.
The solution is to - as far as practical - provide two separate grounds; one quiet one for sensitive signals (denoted by "earth ground" ) and one for high currents (denoted by chassis ground, which doesn't have to be connected to the actual chassis!) The two MUST be tied together - at one, carefully chosen point, sometimes called a "star earth" (useful search term for further reading!)
Thus R1 and R2 provide the voltage feedback to the error amplifier. You don't want to inject large errors via R2, so it is returned to the quiet ground. The error amplifier will take its reference from the "GND" pin (again on the quiet ground)
Now...
Switching current through L imposes a huge AC current waveform on Vin, and generates a huge AC current on Vout respectively. These currents are communicated to ground via C1 and C2 respectively.
In fact the power side of this circuit can be read as one continuous loop GND -> C1 -> L1 -> (switch inside chip between L and Vout) -> C2 -> GND.
This loop is the most important part of the circuit and must be kept as small as possible. Best thing to do is to put the GND leads of C1 and C2 right next to each other - virtually all the AC current goes from one C pin directly to the other. The other connections (PGND, VAUX via C3) are less important but go to this point too.
And one (reasonably thick) trace from here to the low noise ground will carry relatively little current, with relatively little noise on it.
Learning to read this high current path and keep it separate from low noise ground will go a long way to making your switchers trouble free.
I'm not aware of a standard symbol for a pressure sensor.
Usually, it's drawn as an IC.
It's a good idea to indicate in the schematic that this is a sensor, and therefore something special. You can make a text block next to the symbol saying what the sensor is sensing. If you know what kind of sensing element the sensor is based on, you can draw an icon of the sensing element in the schematic symbol. If it's a MEMS pressure sensor like yours, you can draw a bridge on it. (Another example. If you know that some other sensor is based on a phototransistor, you can draw a phototransistor on it.)
Best Answer
I wouldn't use the "earth" symbol unless I meant mains earth or Earth.
There are various ground symbols available.
Figure 1. From Ground, earth and chassis explained (by me).
In your case I would probably use the hollow ground symbol for the real ground and the solid ground symbol for the virtual ground.
Figure 2. Different ground symbols for primary ground and virtual ground.
Notes:
From the comments:
Virtual ground appears to have several meanings. In the inverting amplifier op-amp configuration it refers to the inverting input as being very close to ground potential due to the high gain and negative feedback. In this case of Figure 2, below, and the OP's question it is a ground or reference for the audio signals and they alternate above and below that reference voltage and are equal to that reference voltage when the audio is quiescent.
The term seems to have high-level approval. See TI's datasheet for TLE2426, The "Rail Splitter precision virtual ground" device.
Figure 3. The Belton-Brick uses a virtual ground reference, VB, for biasing all all the op-amps in the audio signal chain to half-supply to allow for alternating audio voltages. (Double-click for high resolution.) Source: Hot Bottles.